1. Field of the Invention
The invention relates to semiconductor structures and somewhat more particularly to semiconductor structures having a plurality of insulating layers one on top of the other with a conductor path therebetween along with unmasked contact points and methods of producing such semiconductor structures whereby select points of the conductor path are unmasked for access to external electrical connection means.
2. Prior Art
German Offenlegungsschrift No. 2,221,072, dated Nov. 9, 1972, suggests a method of producing a semiconductor structure wherein a surface of a semiconductor body is coated with a first organic insulating layer, a conductor path is provided on the first insulating layer, an organic intermediate layer is coated on select portions of the conductor path, a second inorganic insulating layer is coated on all exposed surfaces of the various layers and the entire structure is heated to relatively high temperatures sufficient to expand or oxidize the organic intermediate layer and remove the areas of the second insulating layer which superimposed the intermediate layer so as to unmask the select portions of the conductor path.
In practicing such prior art method, one may utilize, for example, a monocrystalline silicon disk or body in which one or more pn-junctions have been provided, such as by selective diffusion or implantation of doping material during the formation of p- or n-zones. A mask, preferably composed of SiO.sub.2 may be applied onto such a disk to localize the penetration of the dopants at selected areas of the disk and such mask may remain on the finished structure as a first insulating protective layer on the surface of the semiconductor body and be provided with contact windows leading to individual zones or areas of the body for contact thereof by external electrical elements or the like. The electrodes which contact the individual zones of the semiconductor body in a blocking-free manner may then be inserted into appropriate contact windows in a conventional manner. Simultaneously, such insulating protective layer serves as a support for a conductor path leading to select electrodes of the semiconductor body.
In order to provide better protection for an arrangement as described above, it is known to completely cover such an arrangement with a second insulating layer, preferably also composed of an inorganic insulating material. The points of the conductor paths which are to be accessible for external electrical connection means must be uncovered or unmasked from the aforesaid second insulating layer. For this reason, German Offenlegungsschrift No. 2,221,072 suggests applying a layer of an organic polymer, i.e., a photo-resist or lacquer in a suitable pattern on the conductor paths, on those areas of the conductor paths which correspond to the connection points, and then temporarily overcoating such organic layer with the second insulating layer. Thereafter, when such a structure is heated, the organic or polymer layer expands or oxidizes and causes a peeling or removal of portions of the second insulating layer which were located directly above the polymer layer.
An alternative method of exposing or unmasking desired contact points involves the use of a photo-lacquer-etching technique. However, such an alternative method requires the use of liquid, such as a hydrofluoric acid-containing liquid, as an etching means. Such liquid etchants may accidentally etch through a conductor path as well as through the lowermost insulating layer. Further, such etchants have a tendency to expand between the two insulating layers due to capillary forces along the conductor paths and to corrode the conductor paths. The initially described method avoids these drawbacks.
However, the initially described method functions only with relatively large connection points, and even then, practical application thereof requires the use of ultrasonic vibrations and heating to temperatures of at least 520.degree. C. so as to insure sufficient decomposition/vaporization of the organic or polymer layer and the removal of the overlying areas of the organic insulating layer.